The present invention relates to a pyridine-free Karl-Fischer reagent useful for the determination of water and also to a process for the determination of water using this reagent. Conventional reagents consist of a solvent solution for the sample to be examined and a titrating agent. The solvent solution contains sulfur dioxide and an amine, classically pyridine, in a solvent, and the titrating agent contains iodine in a solvent.
A number of suggestions for replacing pyridine in a Karl-Fischer reagent are known from the literature. In Anal. Chim. Acta, 94, 395 (1977), sodium acetate is used as a replacement for pyridine. However, this replacement is accompanied by certain disadvantages. For example, acetates are formed with the alcohol used as the solvent with water being released. Of course this water is troublesome in a method for the determination of water.
The use of amines in place of pyridine has also been described. See, for example, J. Amer. Chem. Soc., 61, 2,407 (1939). However, it was established that the stability of these solutions is very poor in comparison with pyridine-containing solutions. Furthermore, in the case of triethanolamine, the decomposition of the reagent, even in the manufacturing stage, can hardly be prevented.
Furthermore, in Anal. Chem., 28, 1,166 (1956), it has been established that no stable end points can be obtained on titration when pyridine is replaced by amines in such reagents. Thus, it appears from the state of the art that the replacement of pyridine by amines is not sensible because these reagents are either unstable or produce incorrect results.